Process of treating sulphide ores of zinc



NQV l, 1932- Y N. c. cHRlsTENsL-:N 1,886,162

PROCESS OF TREATIING SULPHIDE ORES OF ZINC Filed Nov. 2, 1925 3sheets-sheet 1 NOV' 1, 1932. N. c. cHRlsTNsEN 1,886,162

PRCESS OF TREATING SULPHIDE ORES OF ZINC @MMM wf/Waff 5 Sheets-Sheet NOVl, 1932 N. c. cHRlsTENsEN PROCESS OF TREATING SULPHIDE ORES OF ZINCFiled Nov. 2, 1925 INVENTOR.

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Patented Nov. 1, 1932 NIELS C. CHRISTENSEN OF SALT LAKE CITY, UTAHPROCESS OF TREATIN G SULPHIDE CRES 0F ZINC Application led NovemberrI'his process relates to the treatment ot sul hide ores of zinc. 1t isapplicable to the treatment of ores which contain zinc sulphide alone ormixed with other sulphidcs such as galena, pyrite and chalcopyrite, etc.It is especially applicable to thetreatment of the so-called complex ormixed sulphide oresV oi zinc and lead Which as a rule contain silver andother sulpliides such as pyrite or chalcopyrite (and in some cases othersulphides ot copper, nichel or cobalt) mixed With the gal/ena andsphalerite.

1t is the object oil the process to recover the zinc, and silver andalso the other metals, from the ores as precipitates containing the metls or in metallic form.

The process relates particularly to the treatment of Zinc sulphide oreswith chloride solutions which are adapted to the recovery of the Zincfrom such ores as Well the recovery of the silver and lead (and in somecases the copper and other metals mentioned).

fils described in my United States Patents 1,539,711, 1,539,714 and1,539,712, the simple sulphide minerals of lead, silver and copper mayreadily be brought into solution in a concentrated chloride brinecontaining a relatively small percentage of acid in excess ot the amounttheoretically necessary to act on the soluble minerals in the ore. Thelead y be brought into solution in the cold acid brine, but the actionis much more rapid in the hot acid brine, Whereas the copper and silvercan only be brought into solution Within a reasonable time in a hot acidbrine. As noted in my United Stat-es Patents 1,539,713 and 1,572,268,the lead may be dissolved out of mixed lead-zinc sulphide orc With anacid brine, either hot or cold (preferably het), leaving the greaterpart of the Zinc sulphide unattaclred. Even when a large ex cess of acidis used in a hot sodium chloride brine, this chloride solution Will notbring the greater part oi the Zinc from such ores into solution, unlessa relatively very large ratio oi solution to zinc sulphide in the oreleave the i 2, 1925. Serial No. 66,400.

in its original condition, extracting the lead and leaving they greaterpart ot the silver with the zinc sulphide, due to reprecipitation by theZinc sulphide; The fact that in the' case ot ores containing much Zincsulphide V,

the silver remains largely With the residual Zinc sulphide is a serioushandicap to these processes. The tact that only a relatively small partofthe Zinc is dissolved is also a handicap as the zincmust be recoveredin two separate products, one from the solution and the other from thetreated ore.

These defects are overcome by the rocess described in my United Statesatent 1,549,063 which consists in treating the ore with a relativelylarge excess ot hot concen-v trated hydrochloric acid. By this processpractically all the Zinc and silver as ,Well as the lead (also thecopper in chalcocite and the metals in other simple sulphides) aredissolved. This process has the disadvantage of requiringr a largeexcess of acid which must be distilled away from the treated ore inorder to recover the metals from the treated ore and which must becondensed for reuse. This presents some rather diiiicult problems in theapparatus required.

1t is the object of my process to overcome the disadvantages of all theprocesses described above and to recover the Zinc and silver as Wellasthe lead (and copper, etc.) With achloride solution with the use of arelatively small excess of acid (compared with the process described inUnited States Patent 1,549,063). 1 have found that it is` possible todissolve practically all the Zinc and silver in zinc sulphide oresWithout the use of a large excess ot acid by the use of a suitablechloride brine together with the acid. As noted above afsodium chloridebrine is not entirely satisfactory for this purpose. I have foundhowever that it a relatively concentrated hot calcium chloride. brine isused in the treat-ment ot these ores, that practically all the zinc isbrought into solution very rapidly by adding to this brine a relativelysmall excess ot hydrochloric acid over and above the amounttheoretically necessary to dissolve the soluble material in the ore. fewminutes agitation of iinely ground sulphide ores of zinc, either simpleor complex, with such a hot concentrated calcium chloride brinecontaining a small eX- cess of acid, gives a practically completeextraction of the zinc and silver' and lead from the ore in solution aschlorides in the brine. The copper in chalcocite (and the metals ofother simple sulphides mentioned) are also dissolved. Pyrite andchalcopyrite are substantially unattacked. The sulphur combined with thezinc sulphide and galeria (and other sulphides which are attacked) isdriven off as HzS, which is used in the recovery of the dissolved metalsfrom the brine.

The method of treatment by my process is in general as follows: Thefinely ground ore is agitated with a sufficient volume of the hotCalcium chloride brine to carry the lead and zinc chlorides formed inthe treatment of the ore, and enough hydrochloric acid is added to thebrine to react with the acid consuming material in the ore and leave anexcess of acid in the solution. A relatively concentrated brine must beused to secure the best results, as the activity of the acid brinedecreases with dilution. A brine composed of 50 parts of CaCl2 to 100parts of water gives excellent results but brines somewhat more diluteor more concentrated may be used with good results. The finer the ore isground and the hotter the solution the more rapid and complete is thereaction. With ore ground through 200 mesh and the solution near theboiling point only a few minutes is required to dissolve practically allthe zinc, silver and lead (and the copper and in seme cases cobalt andnickel from their simple sul hides). The reactions are indicated as folows:

The pre nant solution is then separated from the resi ual ore (usuallypyrite and quartz). This is preferably done by filtration, though insome cases decantation may be used. The exact procedure used in theseparation of the pregnant solution from the ore will depend upon thenature of the ore, whether it is a Slmple zinc ore or one which containsconsiderable quantities of silver and lead. If the ore contains onlyzinc, the residual acid may be neutralized by the addition of finelyground oxidized zinc ore to the hot acid pulp. If the ore containssilver, there is danger of precipitating some silver out of the solution1f the residual free acid is completely neutralized. With such ores thetreatment with the acid brine is preferably continued until all the B2Sis driven out of the pulp and a small amount of acid is preferablyretained in solution to prevent precipitation of silver in the pulp byany neutralizing agent. Any

neutralizing agent should therefore preferably not be used in sufficientamount to neutralize all the acid unless all the H2S has been removedfrom the solution. If the ore contains lead in any considerable amount,it is also preferable to maintain a small amount of acid in solutionduring filtration to insure complete extraction of the lead. If the acidis 'completely neutralized and there is any 'H2S in the pulp some silverwill be precipitated and some lead may also be precipitated. Anyneutralization of acid previous to filtration should thereforepreferably not take place until the solution of the sulphides iscomplete and the HZS has been drivenfout of the pulp. It should be notedthat the neutralization of the residual acid in this process is not opento the objection which arises in the treatment of complex ores withbrine solutions for the recovery of lead and silver in whichneutralizing the residual acid in the presence of the zinc sulphide inthe treated ore causes the precipitation of the silver as a sulphide bythe undissolved zinc sulphide. In this process the zinc sulphide isdecomposed and the zinc dissolved and if the ILS is driven out of thesolution there is practically no danger of any precipitation of silver(or lead) from solution. The filtration of the hot acid pulp ispreferably carried out with acid proof filters supplied with acid prooffilter media such as porous tubes of fused alumina (trade name alundum),or

silica or porcelain, etc., or asbestos cloths.y

If the ore is such that the acid may be completely neutralized withoutloss of metals in the residual ore material ordinary filter media may beused. If the ore contains considerable lead so that the solution carriesa hi h concentration of P-bCl2, the solution must e kept hot duringfiltration in order to avoid precipitation of the lead chloride.

The pregnant solution may also be separated from the residual ore bydecantation and the washing of the residual ore may be carried out bycounter current decantation. In case the separation of the solution fromthe ore is carried out in this way the same4 precautions as toneutralizing the residual acid as mentioned above must be considered.The same precaution as to maintenance of temperature, in the case ofores carrying much lead, in order to prevent precipitation of PbCl2during decantation must also be observed. In some casesit isadvantageous to treat the ore with the hot acid concentrated brine andafter the treatment is complete to dilute `the pulp with water -(eitherfresh water or preferably with wash water) and thereafter separate thesolution from the residual ore by decantation and wash by countercurrent decantation. This method is especially suitable to oresrelatively low in lead where there is no danger of loss due toprecipitation of PbCl2 by dilution and cooling. lf desired the dilutedsolution may be separated from the ore by filtration instead ofdecantation.

rlhe recovery of the zinc (and also other metals) from chloridesolutions by methods other than electrolytic has been one of thedifficulties which has militated against the treatment of Zinc ores byvarious chloridizing and leaching processes. My preferred method ishowever very simple, direct and ecient. By it the Zinc is recovered in avery pure precipitate and all the other metals may also be recovered inclean separate precipitates, by the use of cheap reagents used inconnection with the l-lgS generated in the process.

My preferred process of recovering the metals from the pregnant brineconsists in a process of selective precipitation by which the metals arerecovered as separate sulphide precipitates. I have found that bypassing HZS into the pregnant chloride solution in the presence offinely divided calcium carbonate, that the metals are selectvelyprecipitated as sulphides in the following order: copper, lead, zinc,iron and manganese. By adding successive proper amounts of finelydivided calcium carbonate and passing H23 into the solution, the copper,lead, Zinc, iron and manganese may thus be precipitated as separate,clean precipitates. 'lhe amount of CaCO-3 used for each successiveprecipitation is determined by analyzing the solution so as to'determinethe quantity of free acid and metals in solution. The copper may beprecipitated with H253 alone if the solution is not too strongly acidbut if the solution is hot and strongly acid the excess acid must beneutralized with @e003 in order to precipitate all of the copper withH25. The acid concentration which will permit precipitation of thecopper will depend on the concentration of the CaClZ in solution and thetemperature of the solution, the higher the concentration in CaClg andthe hotter the solution the lower the acid concentration which willprevent precipitation of the copper sulphide. This also applies to NaClbrines later referred to in regard to this method of precipitation. The7Eb-may be precipitated from hot concentrated brines with H23 only ifthe solution is nearly neutral, but if the brine is cold and dilute thelead may be precipitated from slightly acid brines, the acidconcentration which will prevent the precipitation of PbS decreasingwith increase in brine concentration and rise in temperature. Thedifference in the acid concentrations which will prevent theprecipitation of the copper and lead from the brines as sulphides is solarge that there is no difficulty in securing a selective precipitationof the copper followed by precipitation of the lead.

T he acid concentrations which prevent the precipitation of the Zn, Feand Mn from brines as sulphides are so low that there is no diculty inprecipitating all the lead from approximately neutral brines with HZSwithout precipitating any ZnS, FeS or MnS, since the acid formed by theprecipitation of the PbS from a neutral brine (as indicated in theequation PbCl2lH2S=Fbs+2HCl is sulficient to prevent precipitation ofany ZnS, FeS or MnS, unless the solution contains only a very smallamount of Pb.

The dili'erences in the very small acid concentrations which preventprecipitation of the ZnS, FeS and MnS are, however, suicient to give aclean differential precipitation of the Zn, Fe and Mn by the use of theproper amount sof CaCOS. To precipitate the Zn from solution withoutprecipitating any Fe or ilin it is merely necessary to add slightly lessCaCGS to the solution than the amount chemically equivalent to the Zn insolution, as indicated in the equation ZnClz-l-HZS-t 021603 ZES l` d l-Ill-20, and thereafter pass HZS through the mixture until theprecipitation of the Zn is complete. After the precipitation of the Zn,the precipitation of the iron may be similarly carried out withoutprecipitating any manganese by adding to the solution an amount of CaCO3chemically equivalent to the iron in solution, as indicated by theequation FeClZ-l-ILS-l CaCO32FeS-l- CaCl2+H2O "l- CO2 and passing H intothe mixture unt-il the iron is all precipitated.

lf very pure products are desired the solution should first be saturatedwith HZS and the chemical equivalents of CaCG should then be addedcontinuously, or in small batches, together with more HQS so as tomaintain a very slight acid concentration during the precipitation andthus prevent the precipitation of any of the metal to be precipitated inthe next precipitation step, this very small acid concentration beingmaintained by keeping the precipitation, as indicated in the equationZnCl2+H2S=ZnS+ QHCl, slightly in advance of the neutralization, asindicated in the equation QHCl-l- CaCO3=CaCl2 -l-HQOJVCOZ. High gradeproducts may, however, be made by adding all the CaCOB at once ifslightly less than the chemical equivalent of CaCOg as compared to themetal to be precipitated is used so that a very small amount of acid ispresent the end of each selective precipitation, which prevents theprecipitation of any of the metal to be precipitated in the next step.rllhis precipitation'is rather slow for all of the metals but the Zincand iron are precipitated considerably more rapidly than the manganese.The selective precipitation of the iron and Zinc gives the best resultsin the cold but the final precipitation of the manganese may be mademuch more rapid by heating the solution, but in most cases it may bereferable to precipitate the manganese with CMSDZ. Calcium hydroxide maybe used for this selective precipitation instead of calcium carbonatebut though the action is more rapid it is more dilticult to obtain cleanseparate products and the operation is also more diliicult as the Ca(OH)2 tends to form small lumps or granules which are relatively inactive,and which must be ground up or emulsitied with the solution during thisprecipitation in order to use up all of the Ca(OH) 2. Calciumsulphydrate may also be used for Vthe selective precipitation of themetals from solution but the selective action is not nearly as perfectas the CaCG-HgS combination, or even as the Ca(OH) 2*H2S combination,though fairly good separate products may be obtained by careful additionof the Ca(SH) 2 in successive steps While the solution is Well agitated.Calcium sulphydrate together with finely divided calcium carbonate orcalcium hydroxide may also be used but has the same objections asCMSI-D2, i. e. the greater difficulty of making a clean separation.Various combinations of the foregoing methods may be used, for example,the lead may be recovered with CBSH) 2, or I-IZS alone for ILS andCaCOa, the zinc may be recovered by using calcium carbonate and H25, theiron by using calcium carbonate and H2 (or Ca(OH)2 and HZS) and themanganese with CMSI-D2. An excess of Ca(SH)2 makes the filtration verydifficult and this should therefore be avoided. The precipitates madewith @1G03 and H2S (and also (1a(Oll) 2 and HQS) filter very rapidly andwithout any diiiculty.

In the treatment of ores high in lead my preferred method ofprecipitation is usually to dilute the pregnant solution with the WashWater and then cool the diluted solution to precipitate as much of thelead as possible as PbCl2. After separating the precipitated PbCl2 fromthe diluted brine, the residual free acid is neutralized (with ore orCaCO3) and the residual lead is precipitated with HSS or preferably withCa 2. The lead maybe precipitated from the dilute brine with HQS alonebut with concentrated brine finely divided CaCO, must be used with theHZS to precipitate the lead as PbS. In the treatment of the dilutedbrine with HZS, the lead is first precipitated as a tan coloredsulphochloride which upon continued addition of ILS changes graduallythrough different shades of red to the deep red color of the normalsulphoehloride and finally as the sulphochloride is decomposed by theHZS turns to the black lead sulphide. Ca.(SH)2 precipitates the leadcompletely from either concentrated or diluted brine. A very cleanproduct may be precipitated if only a very slight excess of Ca(SH)2 overthe theoretical amount indicated in the following equation is used inthe diluted (15% to 20% CaClg) brine: 2PbCl2+Ca(SH)2=A2PbSl-Cai0l2+2HC1.V In a very concentrated brine (50g to 60g (la-C12 to100cc H2O) double this amount must be used to secure completeprecipitation. After precipitation of the lead, the zinc, iron, andmanganese are preferably precipitated as described above by Athe use ofcalcium carbonate and ILS, or if desired `with CatOH)2 and ILS, or withCMSI-D2, or any desired combination of these.

In the case of ores which have a considerable amountof soluble iron andmanganese it is sometimes advantageous to give the comminutcd ore apreliminary Wash (either hot or cold) with a dilute hydrochloric acidsolution (Water and HCl alone) to remove these and prevent contaminationof the mill solution containing the zinc (or zinc, silver and lead). Inthis case if the pregnant solution is clean enough after the lead (orsilver and lead) has been removed as described above the zinc may beprecipitated as a clean product with Ca(SH)2 (or with either CaCO3 orCatOH)2 and ILS if desired). The metals may be recovered from thepreliminary wash solution of chlorides, usually carrying zinc, iron andmanganese, by the selective methods of sulphide precipitation abovedescribed, the zinc, iron and manganese being secured as separatesulphide precipitates, by the use of finely divided calcium carbonateand H28 (or CMOH)2 and HZS) or may be precipitated with Ca(SH)2 ifdesired. The resulting dilute CaClg solution is then treated withsuliicient HZSO. to precipitate the calcium as calcium sulphate and theHC1 solution thus regenerated is used for the treatment of more ore.

The CMSH)2 which may be used for precipitation is made by passing ILSfrom the lixiviation of the ore into milk of lime in a suitable tower orspray chamber.

The foregoing methods of recovering the lead, Zinc, iron and manganesefrom the calcium chloride brine or the diluted calcium chloride brine orfrom the chloride wash solution are applicable not only in this processbut are particularly applicable to the recovery of these metals from allchloride brines and chloride wash solutions obtained in the treatment ofraw sulphide ores with acid brines, such as those described in myPatents 1,539,711; 1,539,712; 1,539,714; and 1,539,713, which processesare directed primarily to the recovery of lead or lead and silver fromsulphide ores. In all these processes some zinc is dissolved by the acidbrines in the treatment of complex sulphide ores as Well as considerableamounts of iron and manganese in many cases, and the foref going methodsof recovering these from the sodium chloride and mixed brines used inthese processes constitute valuable methods of cleaning these solutionsand securing valuable by-products therefrom.

The general method of precipitating the lill.

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metals from the clear pregnant solution senarated from the treated oreWill Vary with the metal content of theore treated but is in general asfollows: If the pregnant solution contains silver and also lead inconsiderable quant' siver is preferably preci'l 'tated from solution bybringing the solu` tion into ci tact with metallic lead which rapidlyprecipitates the silver from solution, (lf the solution contains copperthersilver may be precipitated with copper and the copper Wit-h lead);The greater part-of the lead is then precipitated from solution as PbCl2by cooling or preferably bv diluting` and cooling` the brine. This isbest carried out by adding the Wash Water from the filtering and Washingoperation to the hot brineand passing :ii/current of cold air through aspray of the diluted brine formed as described in my United StatesFatents #21,462,363 and lAelLOSl. The cold solution still contain# asmall percentage of Pb, as yell the zinc and other metalsdissolved outof the re, may then be treated for the recovery of these follows: Theresidual acid in the solution is preferably neutralized by treatmentwith finely ground sulphide ore (which is later treated as describedabove) or with finely ground ox'. lized zinc ore or with calciumcarbonate if desired. HES mace from the acid brine treatment of sulphideore is then passed through the solution precipitating out all the leadas PbS. (First as the pliochloride Which is changed to the sule. byfurther treatment with H25.) This ,-referably carried out by passing theHBS through a spray of the solution as mentioned l ive. `lf the brine isnot sufiiciently diluted i, may be necessary to add some finely di "ledoxidized zinc ore zinc oxide or carvif u bonnie) er limestone to thesolution during the passage of the H25 in order to neutralize the acidformed and secure complete precipitation of the lead. The reactions areindicated below:

his means all the lead may be precipi- Ll from relatively concentratedbrines by ans of HS. The lead may also be cometely removed from th brineby agitating vith zinc sulphide previously precipitated from the brineused in the process, as indicated in the following chemical equation,-

and ilo. 1,572,268 (precipitated FeS or l\ is precipitated as a sulphideas indicated beloW, the CaCO3 neutralizing the acid formed by the actionof the HZS on the ZnCl2 in solution.

ZnClg -t 021.003 -I- HES ZnS -t CaCl2 HZCOS lf the proper proportion ofCaCO-i to ZnCl2 in solution is used practically all the zinc may beprecipitated as a clean White zinc sulphide even though the solutioncontainsa considerable amount of iron and manganese. Any small amount ofCaCOS left with the may readily be dissolved away by treatnient withvery dilute HCl, or preferably With acetic acid, giving a pure White ZnSwhich should be as valuable as Zn() for malring paints and enamels orfor use in the manufacture of linoleuin, rubber goods, etc., as isextremely line and has many of the qualities of Zn@ in a very highdegree. If desired, calcium hydroxide may be used instead of CaCOs butis more difficult to use because of its tendency to agglomerate duringthe treatment thusv requiring grinding or emulsifying in order to use upall the lime and prevent contamination of the precipitated ZnS with anexcessive amount of CatGl-l).2 and CaS. The separation with CatHh isalso not as clean cut as When CnC()s is used.

IAfter filtering out the precipitated ZnS the solution may be treated'with more finely diylled CaCOS and HQS to precipitate the iron out ofthe solution. If the right proportion of CaCO3 to iron in solution (i.e. a chemical equivalent or slightly less), is used practically all theiron' may be precipitated as a black sulphide containing practically nomanganese, even though4 the solution conn tains a considerable amount ofmanganese. lf desired @MOHM may be used instead of Cri-CGS but has theobjectionable features AAentioned above and does not give as clean a.separation between the different metals as After filtering out theprecipitated iron sulphide, the solution may be treated With morecalcium carbonate and HQS as described to precipitate out the manganese,which is precipitated as a clean flesh colored precipitate of MnS. Ifdesired Ca(OH)2 may be used instead of CaCO3 but the CaCOa remains in adispersed condition and does not require grinding to break up thegranules such as are formed when Ca(OI-l) 2 is used. In all these caseshowever the precipitation with CaCO3 and H-JS requires a' somewhatlonger time than the precipitation with Ca(OH)2 and HZS, but this, ismore than compensated for by the avoidance of the necessity for`grinding to break up the granules formed When @MOHM is used and thecleaner separation of the metals.

A remarkable feature of this differential precipitation of PbS, ZnS, FeSand MnS with HZS in the presence of CaCO;s (or Ca(OH)2) is that all ofthese precipitates filter rapidly without any difficulty-giving a clearfiltrate.

If it is desired to produce very high grade clean products of twosulphides ZnS and F eS, and EeS and MnS may be made at the end of theZnand Fe precipitations in order to separate the clean products. These maybe discarded or used in the next clean precipitations, the FeS in theZnS-F eS mixture being used to recipitate ZnS and the MnS in the FeS nSmixture being used to precipitate FeS.

It is obvious that the zinc and iron and manganese need not beselectively precipitated as described but may be precipitated togetheror in different combinates or roups if desired by using HZS and CaCs (orCa(OH) 2) or by using Ca(SH) 2. The silver may also bepprecipitated as asulphide by means of HQS or HES and CaCOa (or Ca(OH)2) in the samemanner as described for the lead or the silver may be precipitated bymeans of PbS or Zn (or FeS or MnS) if desired instead of using lead asdescribed. It will be apparent that the method used will depend upon thecharacter of the ore and the amount of the various metals taken intosolution during the treatment. It is therefore apparent that all thedifferent possible variations in the above method of precipitating themetal and cleaning the solutions cannot be described in detail in thescope of a patent specification.

The precipitated FeS and MnS obtained in cleaning the mill solution areeasily and completely roasted to Feu()3 and MngO3 giving a very finelydivided brilliant red iron oxide and a very finely divided rich brownmanganous oxide, both of which are valuable as pigments.

If it is desired to recover the sulphur as -HZS from the FeS and MnSprecipitates they may be heated in an atmosphere of superheated steamgiving the lower oxides of iron and manganesefwhich quickly oxidize tothe higher oxides in the presence of air) as shown by the followingequations:

FeS -l- H2O FeO HES MnS H2O: MnO -l- HES In all these methods ofprecipitatin the metals as sulphides by the use of H2 and calciumcarbonate or calcium hydroxide or with Calcium sulphyd rate, thechlorine which was combined with the precipitated metals in the solutionremains in the solution as c alcium chloride after the precipitation.The HC1 used in the dissolving of the zinc and other metals maytherefore be easily and cheaply recovered by treating a portion of thecalcium chloride solution with sulphuric acid, so as to decompose theCaCl2 and secure HC1 and CaSO4. This may be done in solution and theCas()4 be filtered out if only a relatively small amount of HCl is usedin the treatment of the ore, but is preferably carried out by treating aportion of the concentrated CaCl2 brine in an iron pot with concentratedHISO., and heating slightly to drive off all the HCl. The water and HC1thus driven out of a 50% CaClz solution may be condensed together togive a HC1 solution carrying from 20% to 30% HC1 depending on theconcentration of the H2SO4 used. In this way the expense ofmanufacturing the HC1 from NaCl and H,SO, is avoided and the acid isrecovered from the mill solution.

Other methods of cleaning the solutions and recovering the zinctherefrom may be used. For example after the removal of the lead asdescribed in the foregoing, the iron may be precipitated as ferriehydroxide by adding finely divided CaCO3 to the solution and thoroughlyagitating and aerating the mixture, preferably by means of the spraydevice described in my United States Patent #1,462,363. If desiredCa(OH)2 may be used instead of CaCO3. To hasten the oxidation andprecipitation of the iron chlorine may be passed into the solution orbleaching powder may be used if desired. After filtering out theprecipitated ferrie hydroxide, the manganese may be precipitated as ahydrated oxide by passing chlorine through the solution, or by addingbleaching powder or other strong oxidizing agents. In the cold thisprecipitation of the manganese requires a long period, and is rarelycompleted except by' heating for a considerable time. After the removalof the manganese the solution may be electrolyzed in a diaphragm cell torecover the zinc and the chlorine combined with the latter. Theelectrolysis of the clean ninc chloride brine presents no difiicultiesif the iron and other impurities are removed.

Instead of electrolyzing the clean zinc chloride brine the zinc may, ifdesired, be precipitated therefrom as ZnS by the addition of Ca(SH)2made from the HES generated in the treatment of the ore or by the use ofHZS in the presence kof CaCl or Ca(OH)2 as previously described. Thechlorine. from the electrolysis of the ZnCl2 solution may be used tomake HCl foruse in the process by mixing it with the HQS generated inthe treatment of the ore in a suitable reaction tower or spray chamber.HC1 and sulphur would thus be secured according to the followingreaction:

The electrolysis of the clean zinc chloride brine in a diaphragm cellrequires a relatively very high voltage (f5 to 6 volts) and the cell iscomplicated by the necessity of trapping and removing the chlorine.Satisfactory diaphragms are also difficult to obtain. The zinc shouldalso not be removed beloW 2% or 3% in the solution for satisfactoryelectrolysis and should preferably be maintained near 10% to 15% forbest results. These conditions are ditlicult to maintain in a millsolution.

ln order to overcome these ditliculties l prefer to secure the metallicZinc trom the Zinc sulphide by electrolysis. Tivo methods may be used.rlhe first method consists in electrolyzing the zinc chloride in a hotbrine solution (either CaCl2 or `DlaCl) with a permeable lead anodethrough which the solution is passed at such a rate that the leadchlorine formed :t the aaodeis dissolved in the brine and carried out ofthe cell before it can ditluse to the cathode. Solution carrying zincchloride is added the cell near the cathode and passed through thepermeable lead anode and out of the cell carrying with it, in solution,the bGlg for n d at the anode. To this hot solution precipitated Zincsulphide (obtained from the mill solution as described above) is addedin sullicient quantity to precipitate the lead and regenerate the zincchloride in solution as shown by the following chemical equation:

The Pb-S is settled or filtered out of the solution which :s taonreturned to the cell and passed through the same cycle again. ln thisWay the use of a diaphragm is avoided, a practically constant zinccontent may be maintained in the electrolytic cell. and a very low uol arequired due to the elecpart of the energy ln this Way the greaterusually required in electrolyzing Zinc solutions is supplied oy thecheaper energy ot ing operatic'o i PDS mas7 be dissolved All 'l 1 carbonand lime States Patent 1.539,

metallic zinc may be recovered from the Zinc ,sulphide7 made in thedissolving` the ZnS ution and electrolyzing the Zinc sulphate ution thustor-med and neutralizing suiphuric .cid generatel in .the electrolysisby the addition of the precipiuated ZnS made in the process so as toprevent depletion of the Zinc solution. ln this Way the zinc in solutionmay be maintained at a practically constant concentration and thesolution may be kept practically neutral, both of which are veryadvantageous in the electrolysis of zinc sulphate solutions. rl`hesolution should preferably be circulated through the cells at acomparatively rapid rate and the ZnS should preferably be added outsideof the cells so that the HES generated by the reaction between the ZnSand H ,SO may be collected and recovered il desired and so that anordinary open type of cellinay be f used. By this method the acidcontent of the solution may be keptvery low allowing the use of a veryhigh current density and high temperature Without excessive resolutionof the zinc cathode.

ln the carrying out of my process various methods may be used forheating the solution and pulp but my preferred method consists in firstheating the calcium chloride brine by passing it through a spray tunnelcountercurrent to the hot gases of combustion from an oil or gas or coaldust burner or coal furnace, as described in my United States Patent#1,441,064. By this method the solutions may be eiliciently heatedWithout dilution and Without clogging up of the heating apparatus. Thesolution also be concentrated to any desired amount during the heatingoperation by proper control o1' the amount ot fuel burned.

The nely ground ore is then mixed with the hot brine and this pulpmixture is then preferably heated by passing the pulp through a tunnelcounter-current to hot gases from an oil7 gas or coal dust burner (orcoal furnace) and agitating the pulp during this passage so that thepulp is brought into contact with the hot gases passing over it andbrought practically to the boiling point.V

The desired amount of HCl acid (preterably hot and concentrated) is thenadded to the hot pulp and the mixture is passed through an agitatorWhere the reaction is completed and the HQS driven olii'. In the heatingof the brine and the pulp they concentration of the brine is preferablycarried vto such a point that the Water introduced with the HCl does notreduce the concentration of the brine below that which should bemaintained for the best operating conditions.

It the pulp and acid have been heated to a sufficiently high temperaturein the preliminary heating before reaching the agitator in Which thetreatment vof the ore is completed, no further heating is necessary Withmany ores (it the ores have been ground sulliciently tine) as thereaction is rapid and complete it the agitation is thorough eno-ugh tobreak up the froth and tree the HZS. lf needed or desired the pulp maybe heated in the agitavor? 5.1.,3

tor by the introduction of superheated steam into the pulp, or by thepassage of hot oil through pyrex glass or silica tubes submerged inthepulp, (Merrill system). The heating and agitation ofthe acid pulp shouldpreferably be continued until the reaction is complete and the'HgS isdriven out of the pulp. If this is done a practically completeextraction Vof the zinc, silver, and lead may be secured from finelyground sulphide ores. The pyrite usually found in such ores remainssubstantially unattacked.

AS previously mentioned, the hot pregnant solution is preferablyseparated from the pulp by filtration, though the treatment of the pulpbeyond this point Will depend largel upon the character of the oretreated as to the amount of lead and silver (and soluble impurities)contained in the ore with the zinc. In most casesin which complex oresare treated,euliicient lead will be present to require that thetemperature of the pulp be maintained at a high point so as to preventprecipitation of lead chloride. In this case the hot pulp is preferablyfiltered away from the residue of treated ore, and the metalsprecipitated therefrpm as previously outlined, the washY water fromtheffiltering operation being preferably mixed'rwith the pregnantsolution after the precipitation of the'silver and before theprecipitation of the lead chloride.

If the ore contains a relatively small amount of lead (or the operationis conducted so that the solution carries only a relatively small amountof lead) the pregnant solution may be recovered from the residue of oreby decantation and the residual ore may be Washed by a system ofcounter-current decantation, the wash solution being mixed with thepregnant brine before precipitation of the metals as previouslydescribed. In some cases the hot pulp from the agitation may be dilutedbefore the decanting and washing operation. The neutralization of theacid and treatment by decantation and washing by counter-currentdecantation would have many advantages over filtration if the previoustreatment has eliminated sulphides and HgS'so as to avoid danger of lossby reprecipitation of silverY and lead. WhetherY or not the residualacid left after treatment Vof the ore is neutralized willldepend aspreviouslyY mentioned upon the nature of the ore and the thoroughnesswith Which the HZS is eliminated in thetreatmelnt. If the neutralizationbrings about the'precipitation of any considerable amount of aluminumhydroxide and imagnesium hydroxide a small amount of lead andi silver:will be carried i down with these, but unless HZS is' present complete.If this is done the residual acid Vmay be neutralized with oxidized oreor limestone and the filtration of theY pulp may beYY carried out withordinary cotton filter Ymedia unless too high a concentration of ZnCl2is carried in the mill solution, when filter media use of a large amountof Wash solution and a large amount of dilution Without building up ofthe mill solution.V This is one of the advantages of the above describedmethods of carrying out my process. This feature together With'thecomplete cleaning of the solutions by the method of precipitation withcalcium carbonate (or Ca(OH)2) and ILS described above, and theregeneration of the HC1 from the solution by treatment of a portion ofthe concentrated barren* solution `With H2SO4 makes possible thecarrying out of the process Without loss of reagents or dissolvedmetals, as theoretically no solutions are discarded due to fouling orbuilding up of Wash solutions as in the case with many other proc-YVesses. These features together with the prac-- tically complete recoveryof ail the valuable metals in the ore are advantages over presentmethods of treating complex zinc sulphide ores which will be apparent toall those familiar with the present day metallurgical treatment of theseores. i

The residue of ore left from-the treatment by my process is'usuallysmall in amount and consists in most cases of pyrite and silica. Thegold contained in the ore is also'left with the residue and in somecases a small amount of the silver is locked up in the pyrite so that itcan not bewdissolved. The severe acid treatment to which the pyrite (andother nonsoluble sulphides) has been subjected makes it very amenable toflotation and a practically complete recovery of the gold and pyrite(and residue of silver) from the siliceous gangue may be had by treatingthis residue by fiotation preferably in a slightly acid pulp With a verysmall amount Yof frothing agent.

The three figures of the drawings appended hereto illustrate methodswhich may be used when treating ores of differentJ kinds by my process.Flow sheet, Fig. 1, shows a method of carrying out the process upon highgrade zinc ores carrying afrelatively small amount of lead (or no lead).The incoming ore (usually wet lter cake Vfrom the fine grindingdepartment) is mixed with the barren dilute mill solution in a suitablemixer or pug mill; the mixture then passes through the pulp heater inwhich the excess water is evaporated and the pulp is heated to theboiling point; the hot concentrated pulp together with the requiredamount of HCl passes into the agitator where the mixture is agitateduntil the dissolving operation is completed; from the leaching agitatorthe pulp flows through a counter-current system of thickeners in whichVthe dissolved chlorides are washed out by counter-current decantation,the washed residue ot ore going to dotation or to waste and the pregnantsolution through the silver precipitator in which the Ag is precipitatedupon metallic Pb; the silver-tree pregnant solution then passes to thecleanup department, first through a spray precipitator in contact withHBS (from the leaching agitator) which precipitates the lead as PbS (itthe ,solution is too concentrated at this, point CaCO?, may be added tocomplete the precipitation of the Pb) the precipitated Pbi is separatedout of the solution by means of a suitable filter, or thickener andfilter or thickener alone, and the lead free solution passes through asecond spray chamber in contact with HQS from the leaching operation andfinely divided CaCO?, in proper amount to precipitate the Zinc from thesolution as ZnS; the ZnS is then separated from the solution in asuitable thickener and i'ilter arrangement and the Zinc-tree solution ismixed with more finely divided CaCOS and passed through a third spraychamber in contact with air, the iron being precipitated as ferriehydroxide; the erric hydroxide is tiltered out of the solution which isthen mixed with iinely divided Ca(OH)2 and passed through a fourth spraychamber in contact with air, the manganese being precipitated as amixture of manganese hydroxides: the manganese precipitated is tilt-eredout of the barren solution which is returned to the head oi the circuitand used over again in the treatment of more ore. VA portion of thebarren CaCl2 solution is concentrated (by being passed through a sprayevaporator) and this concentrated CaClZ solution is treated with H2304in the acid plantto make HCl for use in the leaching ot the ore in theagitator together with a small amount of HZSO.; to make up for acidloss'.

Flow sheet, Fig. 2, illustrates a method of treating an ore containingboth lead and zinc in considerable amount. This treatment difters fromthat shown in flow sheet, Fig. l in that the hot pregnant solution isseparated from the leached ore by means of a filter and the hot pregnantsolution is passed through a spray chamber in Contact with hot air, toeliminate any HZS in the solution, b efore passing the solution throughthe silver precipitator and is then mixed with wash water Jfrom thefiltering operation and passed through a spray cooler to precipitatelead chloride which is settled out of the solution and smelted with lime(or iinely divided CaCO3) and carbon (coal dust) in a reverberatoryfurnace giving lead bullion and Callg slag, the latter being dissolvedin the barren mill solution or used in the acid plant to mal-:e HCl forthe leaching operation. The cold low grade lead solution is passed intothe clean-up or precipitation department in which the Pb, Zn, Fe and Mnare precipitated separately in successive spray chambers by means of HZSand finely divided CaCC'3, the precipitated PbS being returned to thehead of the circuit, the precipitated ZnS being dissolved by treatmentwith HCl or H2504 to make ZnClg or ZnSO4t and the HZS from thisoperation being used inthe precipitating department as indicated, theprecipitated FeS and MnS are roasted to make high grade iron oxide andmanganese oxide; the dilute CaCl2'brine is returned to the head of thecircuit and used in the treatment of more ore, a portion however beingwithdrawn to make HCl in the acid plant as described.

Flow sheet, Fig. 3, illustrates the treatment of a high grade lead orecontaining zinc sulphide. It diers from the treatment shown in lowsheet, Fig. 2, principally in that only such a portion of the low gradesolution passes through the clean-up circuit as is necessary to keep theZinc, iron and manganese within working limits in the solution. This isdone by passing the mixture of ore and solution from the mixer into athickener from which a thickened underflow passes to a pulp heater(rotary kiln type) and the clear solution overflow is separated into twoportions, the main portion passing through a spray evaporator and backinto the main mill circuit with the ore entering the pulp heater, andthe other portion passing through the clean-up circuit where the Pb, Zn,Fe and Mn are precipitated with HZS and inely divided CaCO3, the dilutebarren solution from this treatment being concentrated and heated in aspray evaporator and used as a brine wash in the main iilteringoperation and returned to the circuit at the head of the pulp heater.The precipitated PbS is returned to the head of the circuit andredissolved, the ZnS is dissolved with H2SO4 (and this solution may beelectrolyzed by recovery of the Zn as metal) and the HES used in theprecipitating department, the FeS and MnS are roasted to oxides asdescribed. The diluted low grade mill solution from the PbCl2 settler isreturned tothe head of the circuit and used over again as indicated. ThePbClz is smelted with CaCO3 and carbon as deiso scribed and the CaCl2 isutilized in the leachcircuit or acid plant as previously described. Inthis circuit HgSO, may be used instead of HC1 in the leaching agitatorif desired, the HC1 being generated in the pulp andthe CaSO formedpassing out with the Ihed residue.

s 'It is obvious that many other combinations than those described inthese How sheets may be made to meet dilferent conditions in thetreatment of different ores and these flow Sheets are therefore merelyillustrative of the steps in the process and of the apparatus which maybe used in the process and not the only steps or combinations which arepossible.

From the foregoing it will be apparent that my process has a wide lieldof usefulnessvin the treatment of ores containing zinc sulphide and thatthe results obtained by it in the recovery of practically all the metalseither as primary products or by-products are remar able as comparedwith the present day relatively ineiicient and wasteful treatment ofthese complex sulphide ores.

It will be apparent that it is impossible to fully describe the manvariations and differences in method possible in the application of myprocess to various ores of different character, and I do not thereforedesire to be limited entirely by the foregoing description except as thedescription is embodied in the accompanying claims.

Having described my process, what I claim and desire to patent is:

1. The process of treating sulphide ores of zinc containing lead andsilver which con ssts in a itating said comminuted ore together wit ahot concentrated calcium chloride solution containing hydrochloric acidand thereby dissolving the zinc and silver and lead out of said ore insaid solution, separating'the pregnant solution from said ore, andprecipitating the silver from the hot solution with metallic lead andthereafter cooling said solution and precipitating lead therefrom aslead chloride, precipitating the residual lead from the cold solution asa sulphide, und thereafter adding a finely divided calcium carbonate tosaid solution and passing H,S into said mixture and thereby precipithezinc out of said solution as a sulpbd. e.

2. The process of treating zinc sulphide ores which consists inagitating said orc together with a hot concentrated calcium chloridesolution containinghydrochloric acid and thereby dissolving the zinc outof said ore in said solution as a chloride, separating said pregnantsolution from the residue of treated ore, precipitating the zinc andother metals therefrom with calcium carbonate together with HZS derivedfrom such said treatment of such said ore, so as to obtain the metals as'"l sulphides and' leave the chlorine in said solutions as calciumchloride, and treating a portion of the calcium chloride solution withsulphuric acid to make hydrochloric acid and using'said acid withcalcium chloride solution to treat more ore.

3. The process of treating sulphide ores of zinc which consists inagitating said oomminuted ore together with a hot calcium chloridesolution containing hydrochloric acid and thereby dissolving the zincfrom said ore in said solution, separating said pregnant solution fromthe residue of treated ore, and selectively precipitating the zinc, ironand manganese from said solution as sulphide; in the order named byadding successive amounts of finely divided calcium carbonate to saidsolution and passing HZS into said solution.

4. The process of treating zinc-lead sul-k phide ores which consists inagitating the comminuted ore together with a hot concentrated calciumchloride solution, containing approximately parts or more of CaCl2 to100 parts of water and containing an excess of hydrochloric acid andthereby dissolving substantially all of the zinc, lead and silver fromsaid ore in said solution, separating the pregnant solution from theresidue of treated ore, precipitating silver from said solution withmetallic lead, diluting said solution and cooling said diluted solutionand precipitating lead chloride therefrom, precipitating the residuallead from said solution` as a sulphide with HZS from such above saidtreatment of sulphide ore, precipitating zinc from said lead freesolution as a sulphide with HZS from such above said ore treatment, andfinely divided calcium carbonate.

5. The process of treating zinc-lead sulphide ores containing iron whichconsists in agitating the comminuted ore together with a hotkconcentrated calcium chloride solution, containing approximately 50parts or more of CaCl2 to 100 parts of Water and containing an excess ofhydrochloric acid and thereby dissolving substantially all of the zinc,lead and silver from said ore in said solution, separating the pregnantsolution from the residue of treated ore, precipitating silver from saidsolution with metallic lead, diluting said solution and cooling saiddiluted solution and precipitating lead chloride therefrom,precipitatingt-he residuallead from said solution as a sulphide with HZSfrom such above said treatment of sulphide ore, precipitating zinc fromsaid lead free solution as a sulphide With HQS from such above said oretreatment, and finely divided calcium carbonate, and thereafterprecipitating dissolved iron from said solution as a sulphide with HES,from such above said ore treatment, and finely divided calciumvcarbonate.

6. The process of treating zinc-lead sulphide ores containing iron whichconsists in agitating the comminuted ore together With a hotconcentrated calcium chloride solution, containing approximately 50parts or more of CaCl2 to 100 parts of Water and containing an excess ofhydrochloric acid and thereby dissolving substantially all of the Zinc,lead and silver from said ore in said solution, separating the pregnantsolution from the residue of treated ore, precipitating silver from saidsolution With metallic lead, diluting said solution and cooling saiddiluted solution and precipitating lead chloride therefrom,precipitating the residual lead from said solution as a. sulphide WithH255 from such above said treatment of sulphide ore, precipitating zincfrom said lead -tree solution as a sulphide with H2S, from such abovesaid ore treatment, and finely divided calcium carbonate, and thereafterprecipitating dissolved iron from said solution as a. sulphide withH253, from such above said ore treatment, and finely divided calciumcarbonate, precipitating Vdissolved manganese from said solution as asulphide with H255, from such above said ore treatment, and nely dividedcalcium carbonate, and thereafter heating and concentrating saidsolution and using it in the treatment of more ore. y

7. rlie process of treating zinc-lead sulphide ores Which consists inagitating said comminuted ore together With a hot concentrated calciumchloride solution containing approximately 50 parts or more of CaCl2 to100 parts of Water and containing an excess 1 or hydrochloric acid andthereby dissolving substantially all of the zinc, lead and silver fromsaid ore in said solution, separating the pregnant solution from theresidue of treated ore, precipitating silver therefrom with metalliclead, diluting last said solution With Wash Water from the Washing ofsaid treated ore and precipitating the lead from said solution as asulphide by means of H253 from such above said ore treatment andprecipitating the Zinc from said lead free solution as a sulphide bymeans of H2S, from such above said ore treatment, and finely dividedcalcium carbonate.

8. The process of treating zinc-lead sulphide ores which consists inagitating the comminuted ore together with a hot concentrated calciumchloride solution containing approximately 50 parts or more of CaCl2 to100 parts of Water and containing an excess of hydrochloric acid andthereby dissolving substantially all of the Zinc and lead in said ore insaid solution, separating the pregnant solution from said ore anddiluting said solution and neutralizing the residual acid therein andprecipitating the lead therefrom With H2S and thereafter precipitatingthe zinc therefrom as a sulphide by meansof H2S and nely divided calciumcarbonate.

9. The process of treating zinc-lead sulphide ores containing iron whichconsists in agitatino the comminuted ore together With a hotconcentrated calcium chloride solution containing approximately 50 partsor more of CaCl2 to 100 parts of Water and containing in excess ofhydrochloric acid and thereby dissolving substantially all` of thezincand lead in said ore in said solution, separating the pregnantsolution from said ore and 'diluting said solution and neutralizing theresidual acid therein and precipitating the lead therefrom with ILS andthereafter precipitating the zinc therefrom as a sulphide by means ofH255 and iinely divided calcium carbonate, and thereafter precipitatingirony from said solution as a sulphide by means of H2S' and finelydivided calcium carbonate.

l0. rlhe process of treating zinc-lead sulphide ores containing ironwhich consists in agitating the comminuted ore together With a hotconcentrated calciumfchloride solution containing approximately 50 partsor more of CaCl2 to 100 parts of Water and containing an excessofliydrochloric acid and thereby dissolving substantially all of thezinc and lead in said ore in said solution, separating the pregnantsolution from said ore and diluting said solution and neutralizing theresidual acid therein and precipitating the lead therefrom with H25 andthereafter precipitating the zinc therefrom as a sulphide -by means ofH25 and finely divided calcium carbonate, and thereafterprecipitatingiron from said solution as a sulphide by means of H25 and iinely dividedcalcium carbonate, and thereafter precipitating manganese from saidsolution as a sulphide With H28 and finely divided calcium carbonate andconcentrating and heating the residual solution and using it in thetreatment of more ore.

1l. The process of treating zinc-lead sulphide ores Which consists inagitating the coinminuted ore together With a hot concentrated calciumchloride solution containing approximately 50 parts or more of CaCl2 to100 parts of Water and containing an excess of hydrochloric acid andthereby dissolving substantially all of the Zinc, lead and silver fromsaid ore in said solution, separating the pregnant solution from theresidue of treated ore and precipitating lead therefrom by means of H2Sand finely divided calcium carbonate and thereafter precipitating zinctherefrom by means of H2S and nely divided calcium carbonate.

l2. ln the treatment of Zinc-lead sulphide ores With calcium chloridebrines, the precipitation of the lead from the concentrated chloridesolution as a sulphide by adding finely divided calcium carbonate tosaid solution and passing H2S into said mixture.

13. The selective precipitation of Zinc, iron and manganese fromchloride solutions by adding successive amounts of finely divided wikinmcarbonate to said solution and passing HSS intcisaid mixture and therebypreciptating as slphides the metals in said solution in the order namedabove. Y

Mii The selective precipitationi of lead, Zim?, rOn and'manganese fromchloride brines by adding succeiv'e amounts of finely di- Y videdcalciumY carbonate to said solution and passing HZS into said mixtureand thereby pvecipitatingas sulphides the metals in said nsolutiim inthe order' named above.

15. The selective precipitation of zinc from chloride'solutionscontaining iron by adding finely dividedY calcium carbonate to saidsolution and passing HZS into said mix- Y Ature and therebyprecipitating zinc as a sul- Y phide substantially free from iron.

16. The selective precipitation of zinc from chloride solutionscontaining manganese by adding finely divided calcium carbonate to Saidsolution and passing HZS into said mixture and thereby precipitatingzinc as a sul- 'de substantially free from manganese.

r17. The selective precipitation of zinc from chloride solutionscontaining iron and manganese by adding nelyY divided calcium to sa'hjisolution and passing H28 into said mixture and thereby precipitatingzinc as a sulphide substantially free from iron and mangallese.

In testimony whereof I have signedmy name to this s ecification.

NI LS C. CHRISTENSEN.

